What is Conventional Gasoline?
Conventional gasoline is a volatile flammable liquid mixture of hundreds of species of hydrocarbons, obtained from the distillation of crude oil, and used as fuel for internal combustion engines. It is gasoline that has not been modified by adding an oxygenate and has not been chemically reformulated to meet any particular air quality standards. Conventional gasoline is used everywhere in Arizona except Metropolitan Tucson during the winter (October through March) and in Maricopa County (year-round).
What is Oxygenated Gasoline?
An oxygenate is an oxygen-carrying chemical compound. Oxygenated gasoline is a blend of gasoline to which an oxygenate, typically Ethanol or MTBE, has been added. Blending an oxygenate into gasoline promotes more complete combustion of the gasoline, which reduces emissions of carbon monoxide and volatile organic chemicals. In Arizona, oxygenated gasoline is generally used only in metropolitan Tucson during the winter (October through March).
MTBE is an abbreviation for an oxygenate know as Methyl Tertiary Butyl Ether. MTBE has several good qualities when added to gasoline: 1) MTBE adds volume (up to 15 Volume %), 2) It increases the AKI or octane of the gasoline, and 3) it oxygenates the gasoline. At certain levels, MTBE also reduces benzene emissions (a known carcinogen).
What is Ethanol and why is it blended into our gasoline?
Ethanol is an alcohol made from renewable resources such as corn, other grains, food and beverage wastes, and forestry by-products. Ethanol, like MTBE, increases volume and octane levels and oxygenates gasoline.
What is Octane Number (AKI)?
The AKI is a measure of a particular gasoline blend’s ability to resist engine knock. The stickers seen on gasoline dispensers describing the Regular, Midgrade, and Premium grades of gasoline as “87”, “89”, or “91” octane are commonly referred to as octane numbers. However, it is more accurate to refer to those numbers as the Anti-Knock Index value or simply the AKI.
The AKI is determined in a laboratory by operating, under differing operating conditions, two separate single-cylinder engines: a “Research” engine, by which a Research Octane Number (RON) is determined and a “Motor” engine, by which the Motor Octane Number (MON) is determined. The AKI posted on gasoline dispensers is determined by the following mathematical equation: (RON+MON)/2 or (R+M)/2!
Within the combustion chamber of a spark-ignited, internal-combustion engine, a spark plug ignites the air-fuel mixture (atomized gasoline and air). As the resultant flame radiates away from the point of ignition it moves across the top of the piston, quickly and smoothly. If the last bit of air-fuel mixture ignites spontaneously before the flame front reaches it, there is a sudden jump in the pressure within the cylinder. It is that jump in pressure that causes the familiar pinging or knocking sound.
Is Premium (91) gasoline better than Regular (87)?
Not necessarily! A good rule of thumb is to follow the instructions in your vehicle’s owner’s manual. Your vehicle’s engine was designed in such a way as to run on a specific grade of gasoline, so follow the manufacturer’s recommendation.